1. Field of the Invention
The invention relates in general to a leadframe, and more particularly to a leadframe with a chip pad for two-sided stacking and the manufacturing method for the same.
2. Description of the Related Art
Multi-chip package (MCP), a packaging technology attracting more and more attentions recently, integrates several chips of various types or passive pieces into a semiconductor package structure, so that the MCP is more available in functions or higher in capacity. A leadframe with chip pad is a commonly used multi-chip carriage and is conducive to the saving of manufacturing costs. Besides, in order to further reduce package size, a chip or a passive piece is respectively stacked on the upper and the lower surface of the chip pad of the leadframe. However, as the conductive path of the chips inside the package becomes more complicated, it becomes more difficult for the layout of the leads of the leadframe to meet the requirements of the multi-chip.
A multi-chip package structure using the leadframe, “Semi-conductor stacking Package Structure”, is disclosed in Taiwanese Patent Publication No. 486151. Referring to FIG. 1, the package structure at least includes a chip pad 10, a plurality of leads 20, an upper chip 30, a lower chip 40 and a molding compound 60. Both the chip pad 10 and the leads 20 are components of a leadframe. The leads 20 are disposed on the periphery of the chip pad 10. The upper chip 30 is attached onto the upper surface 11 of the chip pad 10. The lower chip 40 is attached onto the lower surface 12 of the chip pad 10. The chip pad 10 being a metal material can only provide simple connection for grounding. The electrical connection between the upper chip 30 and the leads 20 is achieved by a plurality of first bonding wires 51 formed through wire-bonding. The first bonding wires 51 are formed by placing the upper surface 11 of the chip pad 10 upwards. The electrical connection between the lower chip 40 and the leads 20 is achieved by a plurality of second bonding wires 52 formed through wire-bonding. The second bonding wires 52 are formed by placing the lower surface 12 of the chip pad 10 upwards. Then, the molding compound 60 is used to encapsulate the upper chip 30, the lower chip 40, the first bonding wires 51 and the second bonding wires 52, so the wire-bonding step is made even more difficult. Moreover, the number of the chips packed inside a molding compound is limited, the layout of trace can not be too complicated due to the leadframe and bonding wire, neither can a passive piece nor other surface mounting electronic component be integrated into the upper and the lower surface of the chip pad.